The nature of life is mysterious; its effects or manifestations are familiar to all. It is by a study of these manifestations that we try to discover the nature of life itself. From the visible effects we go back to the invisible cause, from the accidents to the nature.

The most usual criterion of life is movement, in particular self-movement. In other words life is the capacity for self-movement.

That is why in philosophical language we define life as that which makes a being naturally capable of self –perfective immanent activity. This is the great difference between living and non-living being. Human beings as the living beings possess immanent activities. An immanent activity is one whose effects remain within the subject which acts. For example the thinking starts in me and its effects remain in me thinking is an immanent activity; so are growing, seeing, willing etc. Whereas, all the activities of the non-living beings are purely transitive. A transitive activity is one whose effects pass into another being. When I throw a ball the effects are passed on to the ball.